It's tough for trees to thrive in the semi-desert Sous valley region of southern Morocco, but scientists have found that some might be getting a helping hand from an unlikely source.

While the local goats have been considered something of a menace because of their fondness for the argan fruit, Spanish ecologists have observed an unusual way in which they might actually be helping - they are constantly spitting out their seeds.

Domesticated goats in the region are inordinately fond of climbing to the precarious tops of argan trees to find fresh forage.

In some arid habitats, such as argan forests, most green vegetation is at the tops of the trees - which can grow 10 metres high.

Local goatherds are known to encourage the activity, pruning the bushy, thorny trees to make it easier for goats to ascend them, and even helping the goats' kids to learn how to climb.

During the bare autumn season in the region, goats can spend three quarters of their foraging time "treetop grazing" in the argan trees.

Argan is popular for the beauty products which feature in argan oil, made from the tree's nuts.

Image:In argan forests, most green vegetation is at the tops of trees. Pic: J Roman/EBD-CSIC

However, the goats don't like the large argan seeds. Like cows, sheep and deer, goats re-chew their food after fermenting it for a while in a specialised stomach, and while ruminating over their cud, the goats have been observed spitting out the argan nuts.

This means they are delivering clean seeds to new ground, wherever the goat has wandered.

Scientists believe that in gaining some distance from the parent tree, the seedling gains a much better chance of survival.

This novel seed dispersal effect is a variation on the mechanism ecologists call "endozoochory", in which seeds more commonly pass all the way through the animal's digestive system before departing at the other end.

The authors suspected that reports of goats dispersing argan seeds by this more common mechanism were mistaken.

The researchers have witnessed sheep, captive red deer and fallow deer spitting seeds while chewing their cud, and suspect this spitting variation on endozoochory may actually be common - and perhaps an essential route of seed spread for some plant species.